While her brother researched the history of the missing horn, Lethe followed Nichart Briffaut to Formido Fortress, where they ambushed a knight of Lodis, Alphonse Loeher. They tortured the young man and even used a truth potion on him but to no avail as the knight did not know the true purpose of Lodis on Ovis.

At the battle of Ostorea Castle Lethe and Cirvante tried to take command of the defense forces but relented the duty to Nichart, who wanted a chance at revenge. Lethe stuck around just long enough to watch the commander fall before she teleported away. The forces of Alphonse had a chance to fight both of the twins at Harmonia however, and defeated them soundly.

The final battle Lethe took place in was in her master's prison within Angel's Headstone. Alphonse defeated the twins for the last time in the presence of Shaher himself.